you are trying to open a database, but at this moment the OpenAccess runtime cannot find a single assembly which was enhanced; therefore no persistent classes are found. The reason is very likely that there is a reference missing to your class library in the configuration (web.config):
<reference assemblyName="MISSING" configRequired="True" />
<backendconfiguration id="mssqlConfiguration" backend="mssql">
And - of course - your class library must have enhancement enabled, otherwise it will give the same exception.
Hope this clarifies / fixes that issue.
the Telerik team
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